Conventionally, a DVD-RAM disk includes data separated on a plurality of tracks, where if more than one track will be read, a track jump process should be performed. The operations of the track jump process include seeking, tracking, and following operations.
FIG. 1 is a flow chart illustrating a related art seeking method. As shown in FIG. 1, Step 101, the seeking method begins. Step 103, reads current address. Step 105, set a PLL circuit or spindle speed according to the address of the target which the optical pick up head will move to. Step 107, calculates the tracks between the current address and the target address. Step 109, check if the track is 0 or not, if yes, enter step 111, which indicates that seeking is completed, if no, enter step 113 to perform a track jumping. After step 113, enter step 115 to see if it is ready or not, if no, enter step 117, which indicates that seeking is failed, if yes, go to step 119 to read current address. Then step 121, check if it is ready or not, if yes, enter step 107, if no, go to step 123 to recovery the error of reading address. After that, go to step 125 to check if it is ready, if yes, go to step 119, if no, go to step 127, which indicates that the reading of address fails.
As shown, in order to increase the data reading efficiency of Physical Identification (PID) of a DVD-RAM disk after a track-jump, the spindle speed and the frequency of a PLL clock are always pre-determined according to the target zone in which the target address locates. In this way, the PLL only needs time to lock the phase in order for the PID to be read quickly. Sometimes, however, the tracking and following operation after the seeking operation may encounter some unexpected errors, and therefore the optical pick-up head slips to an erroneous address. If the erroneous address in which the optical pick-up head locates is near the target zone, the difference between the pre-set PLL frequency and the channel bit frequency associated with the zone in which the optical pick-up head locates is also small, such that the PLL is capable of locking the correct phase under the pre-set PLL frequency and spindle speed described above. In this way, the erroneous address can be read, and then the seeking operation can be performed again to move the optical pick-up head from the erroneous address to the target address.
If the erroneous address is far away from the target zone, the PLL will require a long period of time to lock the correct phase, or will fail to lock the correct phase under the pre-set PLL frequency and spindle speed described above. In this situation, the related art moves the optical pick-up head back to a servo-on area in the inner track of the optical disk, zone 0 for example, and sets the spindle speed and the PLL frequency corresponding to the inner tack. The location of the optical pick-up head in the inner track can be read and then the track-jump process can be performed again to move the optical pick-up head to the target address. This related art procedure is time-consuming, and degrades the disk drive performance.
Another related art method for detecting the location of the optical pick-up head utilizes a stepping motor and a step index. If, however, the stepping motor does not operate as desired, the step index can not indicate the location of the optical pick-up head correctly.
In short, a novel scheme, having a superior performance to related art methods, of detecting the position of an optical pick-up head is needed to solve these aforementioned problems.